1. Field of the Invention
The present invention relates to a conductive member such as a charging member that can be used while being brought into abutment with a photosensitive member in an electrophotographic apparatus, and to an electrophotographic apparatus and a process cartridge.
2. Description of the Related Art
In an electrophotographic image-forming apparatus, a conductive member having a conductive elastic layer has been used in, for example, each of a charging member, a developing member, a transferring member, and a paper-feeding member. It has been desired that such conductive elastic layer have semiconductivity, e.g., an electric resistance value of about 1×103 Ω·cm or more and 1×109 Ω·cm or less in terms of specific volume resistivity. It has been known that a conductive rubber obtained by compounding a base rubber with carbon black is used in the elastic layer.
Japanese Patent Application Laid-Open No. H11-45013 discloses a member for OA equipment including an elastic body layer formed of a semiconductive rubber material whose specific volume resistance has been adjusted by adding carbon black. In addition, Japanese Patent Application Laid-Open No. H11-45013 describes that a carbon black having a nitrogen adsorption specific surface area of 20 to 150 m2/g and a DBP oil absorption of 60 to 180 ml/100 g is used as the carbon black. In addition, an example of the literature describes that a carbon black having a nitrogen adsorption specific surface area of 32 m2/g and a DBP oil absorption of 140 ml/100 g (trade name: SEAST G-SVH; manufactured by TOKAI CARBON CO., LTD.) was used. In addition, Japanese Patent Application Laid-Open No. H11-45013 describes the following concerning the significance of the numerical range of the DBP oil absorption. When the DBP oil absorption is less than 60 ml/100 g, the structure of the carbon black develops to so low a degree that a large amount of the carbon black needs to be added for eliciting conductivity, thereby leading to an increase in rubber hardness. On the other hand, when the DBP oil absorption exceeds 180 ml/100 g, the structure develops to so high a degree that even the compounding of a small amount of the carbon black causes an excessive change in electric resistance value of the elastic layer, thereby making it difficult to adjust the electric resistance.
By the way, it has been generally known that the dispersibility of the carbon black in a rubber can be improved by reducing the specific surface area of the carbon black, i.e., increasing its particle diameter or by increasing the number of its structures. In addition, the degree to which the structure of the carbon black develops can be evaluated by its DBP oil absorption. This is because a percentage of voids between the aggregates of the carbon black has a positive correlation with the structure of the carbon black. In addition, the DBP oil absorption of the carbon black currently on the market is about 40 to 180 ml/100 g.
Therefore, it can be understood that a carbon black excellent in dispersibility in a rubber and having a large DBP oil absorption has been selected as the carbon black described in Japanese Patent Application Laid-Open No. H11-45013.